The present invention relates to a valve element for a safety valve, wherein the safety valve comprises a valve casing, which defines a flow path, a bore through the casing arranged transversally to the flow path together with identical and oppositely directed valve elements movably mounted in the bore.
The invention is particularly suitable for use in a blowout preventer when performing cable, wire or coiled tubing operations in a subsea oil or gas well.
When working in a well it is necessary to establish a safety barrier against blowout. This is placed on the Christmas tree and ensures that the well is under control when the well valves have to be opened in order to gain access to the well. Use is normally made of several valves with different functions, which are stacked on top of one another. A common valve assembly, for example, is composed of a pipe ram, a shear ram and a blind ram.
A disadvantage with the known valves is the great heights they reach due to the fact that several valves are stacked on top of one another.
During intervention in a well use is often made of a wire, cable or string (a so-called xe2x80x9cslick linexe2x80x9d). When a wire is used, on account of the wire""s construction a lubricator has to be employed, i.e. a device where a lubricant is pumped in between the wire and the seal. This lubricant penetrates the wire""s core parts and ensures the necessary sealing, thus preventing well fluids from leaking past the valve. When a cable or string is used, a stuffing box may be employed instead. This is of a much simpler construction.
From U.S. Pat. No. 5,287,879 the combination is previously known of a lubricator and a safety valve for use in wire operations. This comprises two identical but oppositely directed valve elements (xe2x80x9cramsxe2x80x9d), which are moved towards each other in order to close a flow path. In the front of each valve element a special seal is mounted in order to seal round the wire as well as to add a lubricant to the seals. This lubricant penetrates the wire""s core parts and ensures the necessary seal, thus preventing well fluids from leaking past the valve when it is closed.
The advantage of the above-mentioned valve is that it is a combination of lubricator and safety valve, but it is of a complex design, particularly on account of the need for a lubricant. It is therefore desirable to use a cable instead, but to combine a stuffing box with a valve that is strong enough to prevent blowout, has so far been impossible.
Thus it is an object of the invention to provide a valve, which is more compact than the previously known valves. This is achieved by having the valve element split into one or more parts, where each part is independently movable and driven by its own actuator.
A drawback with wire or cable operations is that means must be available both for sealing around the cable or wire and for closing the well. With the present invention the object is achieved that a valve can be given a dual function, whereby it can act as both a sealing valve and a stuffing box.